Power transmission



/ July 7, 1942. Q E 2,288,830

POWER TRANSMISSION Fild June 17, 1940 INVENTORI HUGH C. NYE

ATTORNEY Patcnted'July 7, 1942- POWER TRANSMIS SION Hugh 0. Nye, Detroit, Mich., assignor to Vickers Incorporated, Detroit, Micln, a corporation of Michigan Application June 17, 1940, Serial No. 340,884

3 Claims. (Cl. 60-52) This invention relates to power transmissions particularly to those of the type comprising .two or more fluid pressure energy translating devices, one of which may function as a pump and another as a fluid motor.

The invention is more particularly concerned with a power transmission system incorporating a difierential-area, cylinder-and-piston motor together with control means for directing fluid to the opposite ends of the motor to produce feed and rapid-traverse movement with highest efficiency. In many classes of machine tools, for example, shapers, planers, and breaching machines, it is desirable to utilize a feed movement in one direction and a rapid-traverse movement in the other direction. At the same time it is likewise desirable to have the feeding movement take place in that direction in which the piston rod is in tension. This means that during the feeding movement, when the work to be done is.

usually theheaviest', the oil is fed into the small end of the cylinder where a given volume of fluid will produce a greater piston movement than in the large end. This drawback has heretofore been overcome by connecting both ends of the cylinder together during the return stroke so that the fluid discharged from the small end is added to the volume supplied to the large end. Such a system, however, does not provide independent control of the speed of movement in one direction as compared to that in the other direction where a flxe'd displacement pump is utilized as the source of supply.

Another method of providing for rapid-traverse and feed rates with a fixed displacement pump utilizes a flow-rate controlling mechanism for providing a reduced rate of fluid supply during the feeding movement, the excess volume delivered bythe pump being bypassed without (10-. ing effective work. Systems of this character permit of ready control of the feeding speed without affecting the rapid return speed but have not heretofore utilized a differentialcylinder action.

.It is an object of the present invention to pro-- vide an improved power transmission system for operating a differential piston-and-cylinder motor in which the advantages of both methods of obtaining feed and rapid-traverse movement are utilized.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawing wherein a preferred form of the present invention is clearly shown.

In the drawing the single figure is a diagrammatic view of a power transmission system incorporating a preferred form of the present-invention.

Referring now to the drawing, there is illustrated a differential-area piston-and-cylinder comprising a cylinder l0 having a pistonl2 therein provided with a rod l4 projecting from one end of the cylinder. For the purpose of supplying fluid to operate the motor a flxed displacement pump l6 may be utilized and may be driven from a suitable prime mover such as an electric motor l8. Suitable overload relief mechanism 20 may be provided for limiting the maximum pressure produced by the pump IS. A suction conduit 22 connects the inlet of the pump with a tank or reservoir 24. From the outlet of the pump a supply conduit 26 connects directly and permanently with the small end of the cylinder l0.

A branch supply conduit 28 extends to one port 30 of a three-way directional-control valve designated 32. A second port 34 is connected with the tank by'means of a conduit 36. The center port 38 of the valve 32 connects by means of a conduit 40 with the large end of the cylinder It. .The valve 32 may be provided with a longitudinallyshiftable spool 42 having lands 44 and 46 adapted -to selectively block either the port 30 or the port 34. In its mid position, illustrated, the spool 42 may connect all three ports together and thus effectively bypass the pump It.

For the purpose of controlling the feeding movement of the piston l2 to the right, there is provided a branch circuit comprising a conduit 48 connected with the supply conduit 26 and leading to the inlet port 50 of a hydrostatic flowregulating valve 52. Such a valve per se is well known in the art and may be constructed similarly to the valve illustrated in Figure 2 of British patent to Vickers, No. 399,609. It will sufllce to state that the valve comprises a manually adjustable throttle 54 together with a hydrostatically regulated valve 56 which acts to maintain a predetermined pressure drop across the throttle 54 thus maintaining constant the rate of flow through the valve for any given setting of the throttle 54. The outlet port 58 of the valve 52 connects by a conduit 69 with the conduit 40. Thus the conduits 48 and ill and the valve 52 comprise a bypass across the two ends of the motor I.

In operation,.with the pump it running and the spool 42 in its central position, illustrated,

the full discharge of the pump will be bypassed to tank through conduit 28, ports 30 and 34 of valve 32 and conduit 36.

When it is desired to start the piston on a righthand feeding stroke, ,the spool 42 may be shifted to the right blocking port 30 and leaving port 38 connected to port 34. Under these conditions the full delivery of the pump is directed into conduit 26 where a portion of it goes into the small end of cylinder l and another portion passes to tank through the bypass 4852 60 and through the valve 32. r

f Since the total volume delivered by the pump I6 is a constant value, the setting of the throttle 54 determines what proportion of that delivery is by-passed to the tank and consequently also determines the proportion which is directed to the cylinder l0. Thus by increasing the opening of the throttle 54 the speed of piston I21 will be to the outlet of the pump through freely open' passages. The full volume of the pump passes through conduit 28, valve 32 and conduit 40 to the large end of cylinder l0. Piston I2 accordingly moves to the left discharging oil through conduit 26 where it joins with the pump delivery and enters the conduit 28, thus adding to the volume delivered to the head end ofcylinder II). It will be seen that under these conditions, since thepressure'in conduits 48 and 60 is equal, there Will be no flow through the flow control valve 52 4 because there is no pressure differential to create such flow. In other words," during leftward movement of the piston l2 the by-pass constituted by the conduits 48 and 60 is ineffective although it is open to the same extent as it was during feeding movement to the right.

It will thusbe seen that the present inven- I tion provides an extremely simple circuit utilizing the advantages of differential cylinder action together with the advantages of aflow-rate controller with a fixed displacement pump.

While the form of embodiment of the invention as herein disclosed constitutes .a preferred form,

' it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows: ,1.- A hydraulic power transmission system comprising in combination a differential-area-cylin der-and-piston motor, a fixed displacement pump for supplying fluid to the motor, a conduit forming a permanently open supply line between the pump outlet and the smallend of the motor,

means for selectively connecting the large end of the motor with either the inlet of the pump for a forward feeding stroke or the outlet of the pump for a rapid return stroke, a by-pass permanently connecting the two ends of the motor, and a flow regulating valve in the by-pass effective to bleed a predetermined portion of the volume of fluid delivered by the pump during feeding movement, and ineffective during the rapid return stroke. 2. A hydraulic power transmission system comprising in combination a differential-area cylinder-and-piston motor, a fixed displacement pump for supplying fluid to the motor, a conduit forming a permanently open supply line between the pump outlet and the small end of the motor, a valve connected with the large end of themotor and with the pump inlet and outlet and effective in one .position to connect the large end of the motor with the pump inlet for forward feeding stroke, in a second position to connect the large end of the motor with the pump outlet for a rapid return stroke, and in a third position to connect the pump inlet and outlet together to stop the motor, a by-pass permanently connecting the two 2 ends of the motor, and a flow regulating valve in the loy-pass effectiveto bleed a predetermined .portion of the volume =01 fluid delivered by the pump diiring feeding movement, and ineffective during the rapid return stroke and while the motor is stopped.

3. A hydraulic power transmission system comprising in combination a differential-area cylinder-and-piston motor, a fixed displacement pump for supplying fluid to the motor, a conduit forming a permanently open supply line between the pump outlet and the small end, of the motor, means for selectively connecting the large end of the motor with either the inlet of the pump for a forward feeding stroke or the outlet of the pump for a rapid return stroke, and a conduit forming a by-pass including means for producing a regulated reduced rate of flow therethrough,

the I 

